Stormwater Sampling and the Mysterious Magnesium
By Chris Whitman

Here on Fort Drum, the end of the year means state stormwater paperwork. Annual discharge reports and discharge monitoring reports are completed; outlining what went well and what outfalls had exceedances for the year. Outfall 5, which is located near the hazardous waste building has historically tested extremely high for magnesium. In years past it was thought this was caused by the dumping of salt near the sampling location, as it was located near a snowplow turn around. To address this issue, snowplows were steered away from this sample location in hopes of correcting the magnesium exceedance.

Stormwater samples this year once again showed high levels of magnesium. Research into the cause led to numerous dead ends. The site was inspected regularly, the area around the sampling location was checked and nothing was found. Earlier this year it popped into my head that this may be a naturally occurring issue due to the geology of the area. Upon some research, I found that limestone can create large deposits of magnesium as it breaks down over time. Fort Drum then contacted a geologist to investigate this idea. He found that dolomite limestone in the area was the primary cause for the magnesium exceedance. Sampling for this location has now been moved and the benchmark stormwater samples this year indicated magnesium levels under the state threshold for the first time in many year.

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